Cathode ray tube



y 2,1939- F. scHRb'rER ET AL 2,

CATHODE RAY TUBE Filed Oct. 19, 1936 INVENTOR v 7/ g M ATTORNEY PatentedMay 2, 1939 UNITED STATES PATENT OFFICE CATHODE RAY TUBE ApplicationOctober 19, 1936, Serial No. 106,301

In Germany Claims.

This invention relates to electric signalling, and in particular, tofacsimile and television transmission systems utilizing cathode raytubes.

In certain types of transmission it is desirable 5 to scan a stillpicture or sign either for testing purposes, advertising, or forpurposes of identification. For example, in a television transmittingstation it is desirable at the end of a program to identify the stationtransmitting. This identification would comprise the call letters of thestation and might include some symbol used as a trade-mark by thestation. Such a symbol or picture may well be a half-tone picture.

Instead of using the studio scanner for scanning a picture surface ofthis, sort, this invention teaches the use of a special scanner whichmakes use of the different secondary emission properties of two or morematerials. According to this invention, the picture support is made ofone material while the picture proper engraved, embossed or raisedthereon is made of another material.

A cathode ray scans the picture area and depending upon whether the rayimpinges an elemental area of the support or the picture proper, more orless electrons will be released in accordance with the secondaryemission properties of the materials making up the support and thepicture.

An electrode serves to capture the released electrons, and theseelectrons serve in turn to produce a voltage representative of theelemental area scan, which voltage may then be amplified by conventionalmeans and used appropriately for transmission.

Accordingly, it is one of the objects of our invention to provide animproved method and means to transmit electro-optical effects.

Another object of our invention is to provide an improved method oftransmitting half-tone pictures.

Another object of our invention is to provide an improved cathode raymethod of transmitting pictures electrically.

A still further object of our invention is to provide an improvedscreened picture transmitting plate for use in cathode ray tubescanners.

Other and ancillary objects will appear upon reading the description andclaims taken together with the drawing in which:

Fig. 1 shows schematically one embodiment of our invention with certainof the associated circuit connections; and

Figs. 2 and 3 show cross-sections of half-tone plates prepared inaccordance with our invention.

October 3, 1935 Referring now to the drawing, our invention will bedescribed in detail.

In Fig. 1 a cathode ray tube I0 is shown comprising a glass bulbdesigned partially as cylinder and as frustum of a cone. Within theglass bulb a cathode ll is arranged equipped with a conventionalelectron optical arrangement for accelerating and for concentrating theelectrons and which is not shown in the drawing since such arrangementsare well known. Furthermore, in the glass bulb I0 two pairs ofdeflecting plates l2 and I3 are arranged as well as an electrode havingthe shape of a frustum of a cone and which may, for instance, bedesigned as wall layer.

Item l5 designates a metal screen arranged at the lower end of the tubeparts formed as cone frustum. The cathode rays emanating from thecathode l l are deflected in such manner by means of the deflectingplates l2, l3 which have sawtooth shaped scanning voltages of differentfrequencies applied thereto, so that the focused point of the cathoderays traces lines on the screen l5 which are closely adjacent eachother, in the manner well known for cathode ray type image scanners fortelevision purposes.

As shown in Fig. 2, the screen [5 may consist of a metal plate formed ofaluminum for'instance, on which the half-tone image is arrangedinaccordance with the half-tone screening method for instance, byphotographic means. The half-tone image then consists, for instance of aconstant number of screened points for each surface unit of the plate l5to be scanned whereby the respective size of the screened ele mentsdepends on the tone value of the respective elemental area of the image.That is tosay, the size of the recessed area is proportional to thedensity of the elemental area of the picture. In a manner similar tothat employed in the making of printing plates, the metal plate l5 canbe subjected to an etching process suchthat for each screen element adepression 20 is produced in the metal plate. These depressions willthen be filled in with a secondary emission material l9 such as carbon,for instance, whose value of secondary emission is smaller than that ofaluminum, and the metal plate I5 is then mounted in the cathode raytube. When the cathode ray moves across the plate l5, it causes at eachsurface element of this screen an emis-- sion of secondary electronswhich depends upon the size of the screen elements. If within a surfaceelement of the plate, a plate element having a very large dimension issituated the secondary emission of this surface element is substantiallydetermined by the material of the plate I5. If however, the ray impingeson a surface element almost completely filled by the secondary emissivematerial I9, a quantity of secondary electrons is produced determined bythe material with which the depressions of the screen are filled in. Thesecondary electrons produced on the screen move towards the electrode Mby the action of the accelerating voltage source designated by IS inFigure 1, since this voltage source produces a field between the screenl5 and electrode M which accelerates the secondary electrons. From theelectrode l6 current flows across the voltage source H5 to the plate I 5and returns to a resistor I? at which the image signals corresponding tothe respective tone value of the elemental areas of the image can bederived. A suitable conventional amplifier may be connected to theterminals [8 for raising the generated signals to an appropriate level.

The plate l5 may also be designed in the manner shown in Fig. 3. Herethe recessed elements 2! consist of approximately cone-shapeddepressions whereby the depth of the individual cones is different anddepends on the tone value of the respective place of the image, whilethe base of the individual cones has approximately the same size for allelements. A screen so designed likewise possesses the property ofemitting secondary electrons depending on theindividual places of theimage, since in fact, the cathode ray impinges on the walls of thecone-shaped depressions at different angles in accordance with the depthof the cone. Therefore in such a plate it is not necessary to use amaterial whose secondary emission property is different from that of theplate metal proper.

A screen according to Fig. 3 may be produced for instance in accordancewith an engraving process for instance in such manner that the image isat first divided into zones having the same half-tone, whereafter withineach zone, cone shaped depressions having a definite depth correspondingto the tone value are worked in by mechanical means or through anetching process.

Finally, a screen of the'type to be used in accordance with theinvention may also be produced by carrying out a division of the imagein accordance with zones having the same gray value and by arrangingwithin each zone for instance with mechanical means, a number ofdepressions per surface unit of the plate, said number depending uponthe density of the elemental area of the picture. This can be done in amanner similar to that known from copper etchings. As in the case of thedepressions mentioned in connection with Fig. 2, these depressions arefilled in with a material having a property of emitting secondaryelectrons different from that of the plate.

Having now described our invention, what we claim is:

l. A cathode ray tube comprising an envelope. means for producing afocused beam of electrons within the envelope, means for deflecting theproduced focused beam of electrons. a planar electrode of predeterminedspecific electron emissivity, said electrode having isolated minuterecessed portions forming a half-tone picture, the areas in the plane ofthe surface of the electrode of said recessed portions corresponding tothe density of elemental areas of the half-tone, and means to collectsecondary electrons emitted from the unrecessed and recessed portions ofthe electrode under the impact of the deflected focused beam.

2. In combination, means for producing a focused beam of electrons, atarget electrode of predetermined specific secondary electronemissivity, said electrode having isolated minute recessed portionsforming a half-tone picture, the areas in the plane of the surface ofthe electrode of said recessed portions corresponding to the density ofelemental areas of the half-tone, means for deflecting the focused beamto scan the electrode and the isolated recessed portions to causesecondary electrons to be emitted from the target and the recessedportions, and means to collect the emitted secondary electrons.

3. A cathode ray tube comprising an envelope, means for producing afocused beam of electrons within the envelope, a planar metallicelectrode of predetermined specific secondary electron emissivity andisolated minute recessed portions forming a half-tone picture, the areasin the plane of the surface of the electrode of said recessed portionscorresponding to the density of elemental areas of the half-tone, asecondary electron emissive material filling for each of the saidrecessed portions, said secondary electron emissive material having aspecific emissivity different from the predetermined specific emissivityof the metallic electrode,- means for deflecting and projecting towardthe electrode the produced focused beam of electrons and electrode meansto collect secondary electrons emitted from the filling material and theelectrode under the impact of the deflected focused beam.

4. An electron device comprising an envelope, an electron gun forproducing a beam of focused electrons positioned within the envelope, ametallic target electrode of predetermined specific secondary electronemissivity positioned in register with the electron gun, a half-tonepicture formed of material with a specific secondary electron emissivitydifferent from that of the target electrode imbedded in the targetelectrode, the areas in the plane of said electrode of said materialcorresponding to the density of the elemental areas of the picture,means intermediate the gun and electrode for scanning the targetelectrode and the half-tone picture therein by the focused beam ofelectrons, and electrode,

means intermediate the target and means for scanning for collectingsecondary electrons emitted from the imbedded half-tone picture and thetarget electrode under the impact of the deflected focused beam ofelectrons.

5. A cathode ray tube comprising an envelope, means for producing afocused beam of electrons within the envelope, means for deflecting theproduced focused beam of electrons, a planar electrode of predeterminedspecific electron emissivity, said electrode having isolated minuteconically recessed portions forming a half-tone picture, the depth ofsaid portions corresponding to the density of the elemental areas of thepicture, and means to collect secondary electrons emitted fromtheunrecessed and recessed portions of the electrode under the impact ofthe deflected focused beam.

FRITZ scHRo'rER. MAX KNOLL.

